1. Field of the Invention
This invention relates to imaging vehicles that are provided with a detector assembly for imaging a scene, and more particularly to the measurement of a 6-axis position and attitude of the imaging vehicle and its detector assembly to improve line-of-sight (LOS) error.
2. Description of the Related Art
An imaging vehicle provides a platform on which a detector assembly is mounted. The vehicle, which includes a propulsion system, may, for example, be a spacecraft, a manned aircraft, an unmanned aerial vehicle (UAV), a missile interceptor, a kinetic energy kill vehicle (KV) interceptor, a land-based vehicle or a ship. The detector assembly includes a telescope (e.g. an optical mirror and/or lens assembly) and one or more detectors that capture images of a scene in the infrared (IR), visible or millimeter wave (MMW) bands of the electromagnetic spectrum. The detector assembly may be single-band or multi-band.
A 6-axis tactical grade or strategic grade Inertial Measurement Unit (IMU) mounted on the vehicle frame provides measurements of both the linear acceleration and angular rate which is processed to give position and attitude of the vehicle. The IMU typically comprises a ring laser gyro, fiber gyro or hemispheric resonator gyro that exhibit good drift performance over a period of time appropriate to the mission duration. Mechanical isolation is commonly used to mechanically low-pass filter the vibrations and body motion observed by the main IMU. Generally the inertial instrument block (gyroscopes and accelerometers) is center of gravity mounted with mechanical isolators within an outer case; the net structure is then termed the IMU. The IMU measures linear acceleration along the orthogonal x, y and z axes and rate of change of angle (roll, pitch and yaw) about those axis to determine the 6-axis position and attitude of the seeker for guidance, navigation and control (GNC) maneuvers. A line extending from the center of the optical system out a great distance to an object in the center of the field of view (FOV) may also be referred to as the line-of-sight (LOS).